STOCK-BASED COMPENSATION - Summary of Restricted Stock Activity (Details) - Restricted Stock - $ / shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Number of Shares
Balance beginning of period (in shares)	1,845,627
Granted (in shares)	593,705	794,700	1,105,010
Vested (in shares)	(633,645)
Forfeited (in shares)	(310,123)
Balance end of period (in shares)	1,495,564	1,845,627
Weighted Average Grant Date Fair Value
Balance beginning of period (in usd per share)	$ 17.11
Granted (in usd per share)	24.79
Vested (in usd per share)	16.49
Forfeited (in usd per share)	18.50
Balance end of period (in usd per share)	$ 20.77	$ 17.11

The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Gross number of share options (or share units) granted during the period.

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Number of options outstanding, including both vested and non-vested options.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Number of share options (or share units) exercised during the current period.

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